Plastic packaging, including broadly molded or formed plastics, may be manufactured from thermoplastic materials. Plastic packaging broadly includes various products and product lines, such as containers for food, solids and semi-solids of various compositions, water, beverages, hot and cold fluids of many kinds, medicines, powders, lotions, creams, agricultural substances and crops, dry and wet chemicals in wide varieties.
Plastic packaging may be produced from non-biodegradable materials. Owing to its nature of use, plastic packaging becomes relatively useless after the contents of the plastic packaging have served their intended purpose. Such spent plastic packaging is discarded after use. Polypropylenes (PP), polyethylenes (PE), and polystyrenes (PS) have high caloric values and upon incineration may damage contemporary incinerators. Polyvinyl chloride (PVC) upon incineration produces toxic gases. Landfill or ocean dumping of these plastic containers also has concomitant problems. These spent containers, made from plastics having high chemical stability, being mostly non-biodegradable, accumulate within landfills and into the waterways and oceans. A major negative side effect of such accumulation is that plastics may leach their chemical additives and molecular break-down products into the environment. Many of these chemical additives are smaller molecules than the original polymers, are toxic to life and interfere with the life-cycles of many organisms. The stability of the plastics used for the manufacture of containers and other items, means they cannot be safely and efficiently burned, they accumulate in the environment, thus, will overburden the landfills and mar the landscape, and they are a source of toxic effluents, leached into the environment.
In the manufacture of plastics and plastic items, the plastic industry is limited to and by the chemical and physical properties of the plastics/polymers. A variety of thermoplastic substances include yet are not limited to polylactic acids (PLA), polypropylenes (PP), polyethylenes (PE), polyesters, aliphatic polyesters, aromatic polyesters, polyolefins, polyvinyl chloride (PVC), polystyrene (PS), and/or polyethylene terephthalate (PET). Long chain molecules may be produced using reactions that incorporate simple ‘sub-unit’ molecules into the polymer by ‘attaching,’ e.g., forming a chemical bond, a sub-unit molecule to another subunit molecule thus forming a small portion of the final polymer. Reactions attach more sub-units to the growing chain, thus, forming a long chain polymer. Several different sub-unit molecules can also be incorporated to form a long chain polymer. The production of complex polymers may be limited only by the type of sub-unit molecules used and/or the type of chemical reactions employed to accomplish the creation of the final polymer.
Polymers exhibit one or more of the following physical and chemical characteristics: some have a low melting point, some have a high melting point, some are hard, some are soft, some are adhesive, some are non-adhesive, some are clear, some are opaque, some are flexible, and some are brittle. Specific polymers may be selected for the manufacture of specific items because the polymer's inherent characteristics are amenable to the manufacture of the specific item. For example; bags may be made from flexible plastics, so the bags will flex and become useful for carrying items within a bag, non-stick pots and pans may be coated with plastics that are essentially non-adhesive, such that foodstuffs do not stick to the pots and pans, permitting easy cleaning, also, clear plastics may be used for packaging so that the intended contents of the package are visible.
Industrial practice has shown that the combination of two or more types of polymers may produce a thermoplastic with characteristics intermediate to the original polymers. Sometimes, while the mixing of two or more polymer types may demonstrate some desired intermediate characteristic, such as a specific viscosity of the melted polymer mixture, another unwanted characteristic may emerge, such that the mixture of two or more polymer types may exhibit, upon cooling, a brittleness, not found in either or any of the original polymer types added to form the mixture.
Industrial practice has found that other compounds may also impart physical and chemical characteristics whenever are blended with polymers. Such additives are commonly included in the production of thermoplastic polymer resins, and include for example compatibility agents, the presence of which permit two or more dissimilar or incompatible polymers to be blended and form a reasonably uniform material, stabilizers, antioxidants, UV absorbers, antistatic agents, conductive agents, foaming agents, nucleating agents, pigmenting agents, melt agents added to lower the melting characteristics of particular thermoplastics, release agents, plasticizers, bulking agents, perfumes, and similar chemicals and materials within the entirety or part of the final product. The introduction of gas or gas bubbles into molten plastics is used to produce foam forms of said plastics. These processes alter the physical characteristics of the base resins. For example, the density of the foam form of any plastic is reduced compared to the solid form of the same plastic. A common example of this is polystyrene foam, often used as a non-biodegradable packing container or packaging fill. Many of these additives and additive agents are small molecules compared with the polymers, and many are toxic to biologic lifeforms. Some are carcinogenic to humans and other mammals, and over time these additives and additive agents leach out of the plastic polymer matrix of the manufactured items into the environment.
One solution to the above mentioned problems associated with the disposal of plastic items is the development of biodegradable plastics. Such plastic polymers would over time decompose into smaller naturally occurring molecules, such molecules being easily incorporated into the life-cycles of organisms without untoward toxic effects.
Polylactic acid is one such biodegradable polymer. The basic building block for this polymer is lactic acid, derived from plant sources not from petroleum sources. Several types of biodegradable polylactic acid polymers are known. They undergo hydrolysis over time whenever exposed to natural conditions found in earth and water. Thus, these polymers will not accumulate within landfills. They will decompose into harmless non-toxic molecules in landfills.
Polylactic acid plastics are low in heat resistance and generally exhibit low glass-transition temperatures making them generally unsuitable for use where the manufactured items may come in contact with elevated temperatures, such as hot foods, hot beverages, or boiling water. Storage and shipping conditions where elevated temperatures may occur have precluded the use of polylactic acid polymer items. Several methods and processes have been developed to make PLA more amenable to being used in thermoforming manufacturing. For example, molten PLA may be held at elevated temperatures in a mold while the polymer slowly crystallizes. In some embodiments, this method requires heat expenditure to warm the mold along with longer ‘dwell’ times within the mold, to impart some heat resistance to the product made from PLA. The additional heat and manufacturing time may raise the cost of manufacturing using this method. Annealing of the manufactured item (e.g., post-crystallizing annealing) can also be used. This method, however, also an additional manufacturing step, requires additional heating and often, if incorrectly applied, causes the manufactured items to physically deform. In some instances, holding the molded or post-mold PLA at elevated temperatures involves the spontaneous production of small spherical bodies within the PLA matrix rendering the manufactured product opaque. Thus, by using these methods, it is difficult to obtain a clear or transparent molded item.
Sheets of PLA and other polymers can be laminated together to produce a composite plastic material. Such methods require twice the manufacturing because they require the production of at least two sheets (one of PLA and one of the other polymer) to be laminated as one final sheet for use in the manufacture of a molded item.
With regard to plastics other than PLA, it was found that recycled mixtures of various plastics from domestic and commercial sources, owing to the variety of polymers from a recycled supply source, are not amenable to thermoforming specific manufactured items requiring a shaping, molding, or extrusion process. The physical mechanical characteristics, i.e., low strength, brittleness, low flexibility, high opacity, etc., of such recycled mixed plastics, are generally undesirable for the manufacture of thermoformed items. While the addition of compatibility agents, such as polystyrol and polybutadiene, can be used to improve the physical mechanical characteristics of such recycled mixtures of various plastics, although mechanically effective, renders the final mixture toxic because these compatibility agents are usually toxic and will leach into the environment, as the recycled plastics are once again in a landfill or improperly discarded into the environment.
Paper and other cellulosic materials are also used as packaging materials for dry goods and under special conditions for liquid goods. Paper and paper products are typically considered to be biodegradable. Cellulose is a hygroscopic material; it absorbs water and many other liquid substances. The utility of paper to be used for the manufacture of containers to convey liquids is limited. Paper typically is manufactured in sheets. As such these sheets must be folded and often folds and edges of such paper sheets must be sealed to other folds and edges to produce a container. Each fold, each sealed seam, requires an extra production step and offers the possibility of structural failure. Additionally, often some plastic coating or laminate is added to the paper, to provide a barrier separating the paper from the potential contents of the container to enable such a paper container to carry liquids or other substances that might be absorbed by the paper alone. Such hybrid paper containers utilize the paper as a structural backbone and the plastic laminate or coating as the barrier for the container. Paper or cellulosic composites are not easily molded in the same manner as thermoformed plastics.